Effect of Substrate Stratification on Growth of Common Nursery Weed Species and Container-grown Ornamental Species

Abstract

Substrate stratification is a method of filling nursery containers with “layers” of different substrates, or different textures of the same substrate. Recently, it has been proposed as a means to improve drainage, substrate moisture dynamics, and optimize nutrient use efficiency. Substrates layered with larger particle bark as the top portion and smaller particle bark as the bottom portion of the container profile would theoretically result in a substrate that dries quickly on the surface, thereby reducing weed germination, but that would also retain adequate moisture for crop growth. The objective of this study was to evaluate the effect of stratified substrates on the growth of common nursery weeds and ornamental crops. This study evaluated the use of coarser bark (<0.5 or 0.75 inches) as the top substrate and finer bark (<0.38 inches) as the bottom substrate with the goal of reducing the water-holding capacity in the top 2 to 3 inches of the substrate to reduce weed germination and growth. Results showed that substrate stratification with more coarse bark on the top decreased the growth of bittercress (Cardamine flexuosa) by 80% to 97%, whereas liverwort (Marchantia polymorpha) coverage was reduced by 95% to 99%. Substrate stratification initially reduced the growth of ligustrum (Ligustrum japonicum) and blue plumbago (Plumbago auriculata), but there was no difference in the shoot or root dry weights of either species in comparison with those of nonstratified industry standard substrates at the end of 24 weeks. The data suggest substrate stratification could be used as an effective weed management strategy for container nursery production.

Single-screen Bark Particle Separation Can be Used to Engineer Stratified Substrate Systems

“…Thus, we are encouraging water retention and distribution to be more uniform throughout the container profile (i.e., promoting water retention in dryer regions and promoting drainage in wetter regions), while maintaining a similar overall porosity. Substrate stratification has also been shown to reduce weed germination (Khamare et al, 2022); however, this strategy involves layering coarse particles on top of finer particles. Thus, the upper portion of the container would dry quickly, inhibiting germination.…”

Effect of Substrate Stratification Without Fine Pine Bark Particles on Growth of Common Nursery Weed Species and Container-grown Ornamental Species

“…Results of our previous study revealed that substrate stratification reduced the growth of bittercress (Cardamine flexuosa) by 80% to 97%, and liverwort (Marchantia polymorpha) coverage was reduced by 95% to 99%. Additionally, there was no difference in the growth of ligustrum (Ligustrum japonicum) and blue plumbago (Plumbago auriculata) in stratified substrates compared with industry-standard substrates (Khamare et al, 2022). Substrate stratification with larger coarse particles as the top strata provides a mulch-like layer that holds less moisture and has no nutrient available for weed seeds to germinate and establish.…”

“…An additional cultural or nonchemical method that could have potential as a weed management tool is "layering" or stratified substrates (Khamare et al, 2022). This is a new area of research in which multiple substrates, or the same substrate with differing physical properties, are layered within a container to accomplish a production goal, such as decreasing water use or nutrient leaching, or potentially reducing weed growth (Criscione et al, 2022;Fields et al, 2021;Khamare et al, 2022).…”

“…An additional cultural or nonchemical method that could have potential as a weed management tool is "layering" or stratified substrates (Khamare et al, 2022). This is a new area of research in which multiple substrates, or the same substrate with differing physical properties, are layered within a container to accomplish a production goal, such as decreasing water use or nutrient leaching, or potentially reducing weed growth (Criscione et al, 2022;Fields et al, 2021;Khamare et al, 2022). Because of the inherent moisture gradient in a container filled uniformly with the same substrate, the upper portion dries quickly, which requires more frequent irrigation to provide enough moisture for recently potted plants to establish, especially soon after transplanting and before roots are fully developed (Fields et al, 2020(Fields et al, , 2021Owen and Altland, 2008).…”

“…In a previous study, we applied the stratification strategy described by Fields et al (2021) inversely to evaluate weed control benefits (Khamare et al, 2022). The larger coarse particles were used as top strata containing no fertilizer, and a fine-textured, highly moisture-retentive substrate comprised the bottom strata.…”